Method and system for cooling an electrolytic cell for aluminum production

ABSTRACT

The invention relates to a cooling method of a igneous electrolytic cell for aluminium production wherein heat transfer fluid droplets (or “divided heat transfer fluid”) are produced, preferentially in a confined volume in contact with a specified surface of at least one wall of the shell of the pot of the electrolytic cell, so as to induce the evaporation of all or part of said droplets by contact with said surface and remove the heat from said surface. The invention also relates to a cooling system capable of implementing the cooling method. The invention makes it possible to obtain a high cooling efficiency due to the latent heat of vaporisation of the heat transfer fluid.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a §371 National Stage Application of InternationalApplication Ser. No. PCT/FR03/002098 filed Jul. 7, 2003 which claimspriority to French Application Ser. No. 02/08629filed Jul. 9, 2002.

BACKGROUND OF THE INVENTION

1. Field of the invention

The invention relates to the production of aluminium by means of igneouselectrolysis, particularly using the Hall-Heroult electrolysis process,and installations intended for the industrial embodiment of saidproduction. The invention relates more specifically to the control ofthermal flows from electrolytic cells and the cooling means used toobtain this control.

2. State of the related art

Metal aluminium is produced industrially by means of igneouselectrolysis, i.e. by electrolysis of alumina in solution in a moltencryolite-based bath, referred to as an electrolyte bath, particularlyaccording to the well-known Hall-Heroult process. The electrolyte bathis contained in pots, referred to as “electrolytic pots”, comprising asteel shell, the inside of which is lined with refractory and/orinsulating materials, and a cathode assembly located at the base of thepot. Anodes are partially immersed in the electrolyte bath. Theexpression “electrolytic cell” normally refers to the assemblycomprising an electrolytic pot and one or more anodes.

The electrolysis current circulating in the electrolyte bath and theliquid aluminium pad via the anodes and the cathode components and whichmay reach intensities greater than 500 kA, carries out alumina reductionreactions and also makes it possible to maintain the electrolyte bath ata temperature of the order of 950° C. by means of the Joule effect. Theelectrolytic cell is fed regularly with alumina so as to compensate forthe alumina consumption resulting from the electrolysis reactions.

The electrolytic cell is generally controlled such that it is in thermalequilibrium, i.e. the heat dissipated by the electrolytic cell iscompensated overall by the heat produced in the cell, which essentiallycomes from the electrolysis current. The thermal equilibrium point isgenerally selected so as to achieve the most favourable operatingconditions in not only technical, but economic terms. In particular, thepossibility to maintain an optimal set-point temperature represents anappreciable saving on the production cost of aluminium due to themaintenance of the current efficiency (or Faraday yield) at a very highvalue, reaching values greater than 95% in the most efficient plants.

The thermal equilibrium conditions depend on the physical parameters ofthe cell (such as the dimensions and nature of the constituent materialsor the electrical resistance of the cell) and the cell operatingconditions (such as the bath temperature or the electrolysis current).The cell is frequently constituted and run so as to induce the formationof a ridge of solidified bath on the lateral walls of the pot, whichparticularly makes it possible to inhibit corrosion of the linings ofsaid walls by the liquid cryolite.

In order to be able to achieve very high electrolysis current values inrestricted electrolytic pot volumes, it is known to equip theelectrolytic cells with specific means to evacuate and dissipate,possibly in a controlled manner, the heat produced by the electrolyticcells.

In particular, in order to favour solidified bath ridge formation morespecifically, it is known, through the American patent U.S. Pat. No.4,087,345, to use a shell equipped with stiffeners and a reinforcementframe constituted so as to favour the cooling of the sides of the pot bynatural convection of ambient air. These static devices do not lendthemselves easily to precise thermal flow control.

It has also been proposed, through the patent application EP 0 047 227,to reinforce the heat insulation of the pot and equip it with heat pipesequipped with heat exchangers. The heat pipes pass through the shell andthe heat insulator and are incorporated in the carbonaceous parts, suchas the edge slabs. This solution is relatively complex and costly toimplement and also results in significant modifications of the pot.

The French patent application FR 2 777 574 (corresponding to theAmerican patent U.S. Pat. No. 6,251,237), held by Aluminium Pechiney,discloses an electrolytic cell cooling device using air blowing withlocalised jets distributed around the shell. However, the very highefficiency of this device is limited by the intrinsic heat capacity ofthe heat transfer fluid.

Having noted the absence of sufficiently satisfactory known solutions,the applicant set an objective to find effective and adaptable means toevacuate and dissipate the heat produced by the electrolytic cell, whichcan easily be implemented and does not require significant modificationof the cell, particularly of the shell, a large infrastructure, orredhibitory additional operating costs. With a view to use the same inboth existing plants and new plants, the applicant particularlyresearched means which make it possible to modify the power of thecells, which can be adapted easily to various cell types or at differentoperating modes of the same cell type, and which lend themselves toindustrial installations comprising a large number of cells in series.

SUMMARY OF THE INVENTION

The invention relates to a method of cooling an igneous electrolyticcell for the production of aluminium wherein a heat transfer fluid (orfluid coolant) absorbs the heat from said cell by a change of phase ofall or part of said fluid in contact with the cell pot.

More specifically, in the method according to the invention, a “dividedheat transfer fluid” (or “divided fluid coolant”) is produced, such asdroplets of a heat transfer fluid, and all or part of said droplets areplaced in contact with the pot shell, so as to induce the vaporisationof all or part of said droplets.

The heat transfer fluid vapour formed by the vaporisation of all or partof said droplets upon contacting the shell may be evacuated by naturalventilation (such as convection), by blowing or by suction.

The vaporisation removes heat from the cell and said heat may then beevacuated with the heat transfer fluid vapour. The divided form of theheat transfer fluid makes it possible to preserve the latent heat ofevaporation of the fluid until it comes into contact with the pot shell.The droplets are heated and vaporised, at least partially, in contactwith the pot shell and the vapour produced in this way carries aquantity of thermal energy wherein a significant proportion correspondsto the latent heat of evaporation of the fluid.

Therefore, the applicant had the idea of benefiting from the high heatabsorption capacity associated with the vaporisation of the droplets toincrease the cooling power of the heat transfer fluid considerably. Inparticular, the formation of heat transfer fluid in divided form in agas makes it possible to obtain a higher heat conductivity, specificheat and latent heat than the gas alone. The applicant also had the ideathat the division or fractionation of the fluid into separate dropletsalso makes it possible to produce a substantially homogeneous, butdiscontinuous heat transfer fluid, which breaks, in particular, theelectrical continuity of the heat transfer fluid, while preserving ahigh heat capacity in the heat transfer fluid.

In a preferred embodiment of the invention, the electrolytic cell isequipped with at least one confinement means forming a confined space inthe vicinity of a specified surface of at least one of the pot shellwalls and heat transfer fluid droplets are produced in said space. Theconfinement means may possibly be in contact with the shell. It maypossibly be contiguous or fixed to the shell or integral therewith.

The invention also relates to a system for cooling an igneouselectrolytic cell for the production of aluminium which is characterisedin that it comprises at least one means to produce heat transfer fluiddroplets, advantageously in the vicinity of the pot shell, and one meansto place said droplets in contact with the shell, so as to induce thevaporisation of all or part of said droplets.

The cooling system according to the invention may also comprise means toevacuate the vaporised heat transfer fluid.

In a preferred embodiment of the invention, the cooling system alsocomprises at least one confinement housing or casing, at least one heattransfer fluid supply means and at least one means to produce dropletsof said fluid in said casing.

The confinement casings, which are typically placed at a specifieddistance from the pot shell favour the contact of the droplets with aspecified surface of the shell. They are preferentially placed in thevicinity of the lateral walls of the shell. They may possibly becontiguous or fixed to the walls of the shell or integral therewith.

Said cooling system is capable of implementing the cooling methodaccording to the invention.

The invention also relates to a method to regulate an electrolytic cellintended to produce aluminium by means of igneous electrolysis includinga cell cooling method according to the invention.

The invention also relates to an electrolytic cell intended to producealuminium by means of igneous electrolysis comprising a cooling systemaccording to the invention.

The invention also relates to the use of the cooling method according tothe invention to cool an igneous electrolysis aluminium production cell.

The invention also relates to the use of the cooling system according tothe invention to cool an igneous electrolysis aluminium production cell.

The invention is particularly applicable to aluminium production bymeans of the Hall-Héroult process.

The invention makes it possible to reduce the thickness of the innerrefractory linings (or “crucible”) of electrolytic cell pots,particularly the lateral walls, and increase the internal volume of thecrucible able to contain the electrolytic bath accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents, in a cross-section view, a typical electrolytic cellfor aluminium production using prebaked anodes made of carbonaceousmaterial.

FIG. 2 illustrates schematically in a cross-section view an electrolyticcell comprising a cooling system according to a preferred embodiment ofthe invention.

FIG. 3 illustrates schematically in a cross-section view a part of thecooling system according to a preferred embodiment of the invention.

FIG. 4 illustrates schematically in a side view an electrolytic cell potequipped with a cooling system according to a preferred embodiment ofthe invention.

FIG. 5 illustrates schematically along the cross-section AA in FIG. 3 anelectrolytic cell equipped with a cooling system according to apreferred embodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

As illustrated in FIG. 1, an electrolytic cell 1 for aluminiumproduction by means of igneous electrolysis typically comprises a pot20, anodes 7 and alumina feed means 11. The anodes are connected by ananode beam 10 by means of support and attachment means 8, 9. The pot 20comprises a metal shell 2, typically made of steel, internal liningcomponents 3, 4 and cathode components 5. The internal lining components3, 4 are generally blocks of refractory materials, which may be, in partor in whole, heat insulators. The cathode components 5 incorporateconnection bars (or cathode bars) 6, typically made of steel, to whichthe electrical conductors used to route the electrolysis current areattached.

The lining components 3, 4 and the cathode components 5 form, inside thepot, a crucible intended to contain the electrolyte bath 13 and a liquidmetal pad 12 when the cell is in operation, during which the anodes 7are partially immersed in the electrolyte bath 13. The electrolyte bathcontains dissolved alumina and, as a general rule, an alumina-basedcovering layer (or crust) 14 covers the electrolyte bath. In someoperating modes, the internal lateral walls 3 may be lined with a layerof solidified bath 15. The lining components 3, 4 frequently consists ofedge slabs made of carbonaceous material or based on carbonaceouscompounds, such as an SiC-base refractory material and lining pastes.

The electrolysis current transits in the electrolyte bath 13 via theanode beam 10, the support and attachment means 8, 9, the anodes 7, thecathode components 5 and the cathode bars 6.

The metal aluminium produced during the electrolysis is normallyaccumulated at the bottom of the pot and a relatively clear interface 19is established between the liquid metal 12 and the molten cryolite-basedbath 13. The position of this bath-metal interface may vary over time:it goes up as the liquid metal is accumulated at the bottom of the potand it goes down when the liquid metal is removed from the pot.

Several electrolytic cells are generally arranged in a line, inbuildings called electrolysis potrooms, and connected electrically inseries using connecting conductors. More specifically, the cathode bars6 of a so-called “upstream” pot are connected electrically to the anodes7 of a so-called “downstream” pot, typically via connecting conductors16, 17, 18 and support and connection means 8, 9, 10 of the anodes 7.The cells are typically arranged so as to form two or more parallellines. The electrolysis current flows in this way in cascade from onecell to the next.

The anodes 7 are typically made of carbonaceous material, even thoughthat may also consist, in part or in whole, of a so-called “inert”non-consumable material, such as a metal material or ceramic/metalcomposite (or “cermet”).

According to the invention, the method of cooling an electrolytic cell 1intended for aluminium production by means of igneous electrolysis, saidcell 1 comprising a pot 20 comprising a metal shell 2 having lateralwalls 21, 22 and at least one bottom wall 23, said pot 20 being intendedto contain an electrolyte bath 13 and a liquid metal pad 12, ischaracterised in that it comprises:

-   -   producing heat transfer fluid droplets,    -   placing all or part of said droplets into contact with the shell        2, so as to induce the vaporisation of all or part of said        droplets.

The vaporisation of all or part of the heat transfer fluid dropletsinduces a transfer of heat from the shell to the heat transfer fluid,which makes it possible to remove heat from the shell and cool it.

Preferentially, said droplets are placed in contact with a specifiedsurface 107 of the shell 2, which makes it possible to select the mostadvantageous surfaces in terms of heat and increase the coolingefficiency of the pot under certain conditions.

The contact with the shell 2 (or a specified surface 107 of the shell)is a thermal contact, in that it makes it possible to remove thermalenergy from the shell by means of the vaporisation of all or part of theheat transfer fluid droplets.

The droplets may be placed in contact with the shell and, morespecifically, the outer surface of the shell, in different ways, such asby confinement in the vicinity of the shell, by channelling, projection,or a combination of said means.

According to a preferred embodiment of the invention, the method ofcooling an electrolytic cell 1 intended for aluminium production bymeans of igneous electrolysis is characterised in that, in addition, theelectrolytic cell 1 is equipped with at least one means 101, referred toas “confinement means”, to form a confined space 102 in the vicinity of(or possibly in contact with) a specified surface 107 of at least one ofthe walls 21, 22, 23 of the shell 2, preferentially at least one of thelateral walls 21, 22 of the shell 2, and in that it comprises theproduction of heat transfer fluid droplets in said space 102, so as toplace all or part of said droplets in contact with said surface 107.

The term “in the vicinity” refers to a distance typically less than 20cm, or even less than 10 cm.

The confinement of the droplets in a specified volume in the vicinity ofa part of the shell, or in contact with said shell, makes it possible tolimit and control the diffusion of said droplets.

The droplets are typically produced at a specified distance D from oneof the walls 21, 22, 23 of the shell 2, i.e. where the divided heattransfer fluid production zone(s) is/are located at a specified distanceD from said wall. The heat transfer fluid is then routed, typically inthe liquid state, to the specified distance D. The droplets arepreferentially formed in the vicinity of the pot shell in order toprevent the coalescence (or agglomeration) of said droplets before thevaporisation thereof in contact with said wall, i.e. the specifieddistance is preferentially short (preferentially less than approximately20 cm, and more preferentially less than 10 cm). Said production zonesare typically located in one or more confinement casings 101.

The droplets may be produced continuously or discontinuously. Theproduction rate of said droplets may be variable. The cooling methodadvantageously comprises the control of the production rate of saiddroplets. The volume proportion of heat transfer fluid droplets may thenbe varied in a controlled manner. This alternative embodiment of theinvention makes it possible to control the heat extraction from the cellprecisely.

Said droplets typically have a size between 0.1 and 5 mm, andpreferentially between 1 and 5 mm. Droplets of a size less thanapproximately 0.1 mm involve the drawback of being easily carried by themovements of the ambient air, or by any evacuation flow of the vaporiseddroplets, before coming into contact with the shell.

In an advantageous embodiment of the invention, the droplets form a mistor aerosol, preferentially a dense aerosol, in order to favour thevaporisation of the droplets and increase the cooling efficiency.

Said droplets are advantageously produced by spraying said heat transferfluid, typically using the liquid phase. This spraying may be carriedout using at least one nozzle.

The heat transfer fluid is advantageously water since this substance hasa very high latent heat of vaporisation. Said water is preferentiallypurified, in order to reduce its electrical conductivity and limitdepositions on the wall of the shell which may, in the long-term, reducethe cooling efficiency. This purification is advantageously carried out,upstream, using a treatment column 113. It typically comprises a waterdeionisation operation. Preferentially, the purified water contains intotal a quantity of ions (anions and cations) less than 10 μg per litreof water and more preferentially less than 1 μg per litre of water.

In a preferred embodiment of the invention, the confinement means 101comprises at least one casing, i.e. the heat transfer fluid is confinedusing at least one casing 101. Said casing is placed at a specifieddistance from the wall of the shell. This embodiment makes it possibleto increase the probability of physical contact between said dropletsand the surface of the shell (and preferentially a specified surface 107of the shell), and prevent the dispersion thereof in the areasurrounding the pot 20. The confinement casing 101 typically has aspecified internal space or volume 102, but it is advantageously open,typically on the side of the shell. It is possible if required tocontrol the droplet formation rate individually in each confinementcasing 101.

The confinement means 101 may be contiguous or fixed on the shell 2 orintegral therewith.

It is advantageous to position said casing 101 so that it overlaps withthe average level of the interface 19 between the electrolyte bath 13and the liquid metal pad 12, i.e. so as to lie on both sides of theaverage level of said interface.

The cooling method according to the invention may also compriseevacuation of all or part of the heat transfer fluid vapour formed bythe vaporisation of all or part of said droplets in contact with theshell 2 (and particularly in contact with said specified surface 107).This evacuation may be carried out by means of natural ventilation, bysuction or blowing, or a combination of said means. The heat transferfluid vapour is typically evacuated continuously.

Preferentially, the vaporised heat transfer fluid is channelled(typically by suction or blowing) to a point at a distance from thepots, which may be located in the same potroom or outside said potroom,where the heat transfer fluid may be cooled if required, so as tocondense the heat transfer fluid vapour, and reintroduced into thecooling circuit.

Advantageously, when the method comprises evacuation of the heattransfer fluid vapour, the droplets are mixed with a carrier gas inorder to facilitate the evacuation of the vaporised heat transfer fluidand favour the evaporation of any heat transfer fluid condensates. Thecarrier gas may be added to said droplets. The carrier gas mayadvantageously be used to produce the heat transfer fluid droplets byspraying. To this end, the carrier gas may be routed in compressed form.The carrier gas is typically air, but it is possible, within the scopeof the invention, to use other gases or gas mixtures.

In a preferred embodiment of the invention, the method comprises thecirculation of a heat transfer fluid, in an open or closed circuit,comprising:

-   -   a first part for the heat transfer fluid supply, i.e. to provide        and route the heat transfer fluid, typically in the liquid        state, to the droplet production zone(s);    -   a second part for the heat transfer fluid droplet formation,        typically in said confined space, and to place the divided heat        transfer fluid in contact with the shell, so as to induce its        complete or partial vaporisation;    -   a third part for the evacuation of the vaporised heat transfer        fluid.

In practice, the evacuated heat transfer fluid typically comprisesvapour and some non-vaporised fine droplets. It may possibly contain aliquid condensate of said heat transfer fluid recovered at a distancefrom the shell.

According to the invention, the cooling system 100 of an electrolyticcell 1 intended for aluminium production by means of igneouselectrolysis, said cell 1 comprising a pot 20 comprising a metal shell 2having lateral walls 21, 22 and at least one bottom wall 23, said pot 20being intended to contain an electrolyte bath 13 and a liquid metal pad12, is characterised in that it comprises at least one means 103 toproduce heat transfer fluid droplets, typically in the vicinity of theshell 2 of the cell 1, and one means 101 to place all or part of saiddroplets in contact with the shell 2, so as to induce the vaporisationof all or part of said droplets.

In a preferred embodiment of the invention, the cooling system 100 of anelectrolytic cell 1 intended for aluminium production by means ofigneous electrolysis is characterised in that it also comprises:

-   -   at least one confinement casing 101 at a specified distance from        at least one of the walls 21, 22, 23 of the shell 2,    -   heat transfer fluid supply means 105, 111, 112, 113, 114,    -   at least one means 103 to produce heat transfer fluid droplets        in said casing, so as to place all or part of said droplets in        contact with the shell 2.

The confinement casings 101 are typically in the vicinity of the walls21, 22, 23 of the shell 2 or, possibly, in contact with the shell 2.They are advantageously placed in the vicinity of, or in contact with,at least one of the lateral walls 21, 22 of said shell 2. The term “inthe vicinity” refers to a specified distance typically less than 20 cm,or less than 10 cm.

The confinement casings 101 may be contiguous or fixed on the shell 2 orintegral therewith.

Each confinement casing 101 forms a confined space 102 typicallycorresponding to a specified internal volume. The confinement casing 101is advantageously open, typically on the side of the shell 2, so as tofavour heat exchanges between the shell and the droplets. Theconfinement casing 101 may possibly be open, particularly, in its upperpart 101 a and/or in its lower part 101 b.

Said system advantageously comprises a plurality of confinement casings101 distributed around the shell 2 and, preferentially, on the lateralwalls 21, 22 of the shell 2. Each confinement casing 101 isadvantageously positioned so as to overlap with the average level of theinterface 19 between the electrolyte bath 13 and the liquid metal pad12. In this case, each casing is typically positioned in a substantiallysymmetric manner with respect to the average level of the interface (theheight H1 above the average level 19 and the height H2 above the averagelevel 19 are in this case substantially equal).

The average depth P of the confinement casings 101 is typically lessthan 20 cm. The height H of the casings, on the side of the surface 107,is typically between 20 cm and 100 cm, or between 20 cm and 80 cm. Thewidth L of the confinement casings 101 may be less than or equal to thespacing E between the stiffeners 25; they may also be incorporated in,or incorporate, said stiffeners. The specified surface area 107 coveredby the casings is typically between 0.2 and 1 m², and more typicallybetween 0.3 and 0.5 m².

The means 103 to produce the droplets is advantageously a sprayingmeans. This means typically comprises at least one nozzle, such as anaerosol nozzle.

The confinement casings may comprise one or more means 103 to producedroplets.

The offset ΔH between the spraying means 103 and the average level 19 ofthe metal bath interface may be positive, zero or negative, i.e. thenozzle may be located above or below the interface level or at the samelevel as said interface.

The heat transfer fluid supply means 105, 111, 112, 113, 114 typicallycomprise routing means 105, 111, 112, 114, such as conduits, and atreatment column 113. The routing means typically comprise adistribution conduit 111, an electrically insulating conduit 112 and aheat transfer fluid supply conduit 114.

Advantageously, the system according to the invention also comprises atleast one means 104, 110, such as a conduit, to supply each confinementcasing 101 with carrier gas, possibly pressurised. Preferentially, italso comprises a means 108, such as a mixer, to produce said dropletsusing said carrier gas.

The cooling system according to the invention advantageously comprisesat least one means 109 to control the heat transfer fluid dropletproduction rate.

The cooling system according to the invention advantageously comprisesmeans 106, 120, 121, 122, 123, 124 to evacuate all or part of thevaporised heat transfer fluid in contact with the shell 2. Theevacuation means make it possible to evacuate the heat transfer fluidvapour formed by the vaporisation of all or part of said droplets cominginto contact with said surface 107.

The evacuation means 106, 120, 121, 122, 123, 124, which typicallycomprise channelling means, are capable of evacuating all or part of theheat transfer fluid vapour after evaporation or vaporisation of all orpart of said droplets in contact with the shell 2. In particular, saidevacuation means typically comprise evacuation conduits 106, 120, 121,124 and a suction or blowing means 123. The evacuation conduitstypically comprise a manifold conduit 120, an electrically insulatingconduit 121 and an outlet conduit 124. The suction and blowing means 123is typically a fan. These means may also comprise a condenser 122 tocondense the suspended heat transfer fluid droplets. This condensationparticularly makes it possible to recover the heat transfer fluid andreintroduce it into the cooling circuit. The condenser mayadvantageously comprise cooling means of the condensed heat transferfluid in order to be able to reintroduce it into the cooling circuit ata specified temperature, which is generally markedly lower than thevaporisation temperature. It is advantageous to provide means to favourthe flow and evacuation of any heat transfer fluid condensates, such asa sloping of some evacuation conduits (particularly in the manifoldconduit 120). The evacuation conduits may comprise a collector 106,which may be positioned in the upper part 101 a or lower part 101 b ofthe casings.

The applicant estimates that the number of confinement casings requiredfor a 350 kA pot is typically between approximately 30 and 60. Thequantity of heat transfer fluid to be supplied to each casing istypically between 25 and 125 l/h. It also estimates that the fraction ofheat transfer fluid droplets actually evaporated in contact with theshell is between 20 and 60%. The evacuated thermal power is typicallybetween 5 and 25 kW/m². The applicant also estimates that, if a carriergas is used, the carrier gas flow rate per casing advantageously istypically between 25 Nm³/h and 150 Nm³/h.

LIST OF NUMERIC REFERENCES

-   -   1 Electrolytic cell    -   2 Shell    -   3 Lateral internal lining    -   4 Base internal lining    -   5 Cathode components    -   6 Connection bar or cathode bar    -   7 Anode    -   8 Anode support means (typically a multipode)    -   9 Anode support and attachment means (stem)    -   10 Anode beam    -   11 Alumina feed means    -   12 Liquid metal pad    -   13 Electrolyte bath    -   14 Alumina covering layer (or crust)    -   15 Solidified bath layer    -   16 Connecting conductor (riser)    -   17 Connecting conductor (collector)    -   18 Connecting conductor    -   19 Interface between liquid metal pad and electrolyte bath    -   20 Pot    -   21 Lateral wall of shell    -   22 End lateral wall of shell    -   23 Bottom wall of shell    -   25 Shell stiffener    -   100 Cooling system    -   101 Confinement casing    -   101 a Upper part of confinement casing    -   101 b Lower part of confinement casing    -   102 Confined space    -   103 Means to produce heat transfer fluid droplets    -   104 Conduit    -   105 Conduit    -   106 Collector    -   107 Cooling surface    -   108 Mixer    -   109 Heat transfer fluid droplet production rate control means    -   110 Carrier gas supply conduit    -   111 Distribution conduit    -   112 Insulating conduit    -   113 Treatment column    -   114 Heat transfer fluid supply conduit    -   120 Manifold conduit    -   121 Insulating conduit    -   122 Condenser    -   123 Suction or blowing means    -   124 Outlet conduit

1. A method of cooling an electrolytic cell intended for aluminiumproduction by means of igneous electrolysis, said cell comprising a potcomprising a metal shell having lateral walls and at least one bottomwall, said pot being intended to contain an electrolyte bath and aliquid metal pad, said method comprising: producing heat transfer fluiddroplets, placing all or part of said droplets in contact with theshell, so as to induce vaporisation of all or part of said droplets. 2.A method according to claim 1, wherein said droplets are placed incontact with the shell by confinement in the vicinity of the shell, bychannelling, projection, or a combination thereof.
 3. A method accordingto claim 1, wherein said droplets are placed in contact with a specifiedsurface of the shell.
 4. A method according to claim 1, wherein theelectrolytic cell is also equipped with at least one confinement meansto form a confined space in the vicinity of, or in contact with, aspecified surface of at least one of the walls of the shell, and whereinsaid method further comprises the production of heat transfer fluiddroplets in said space, so as to place all or part of said droplets incontact with said surface.
 5. A method according to claim 4, wherein theconfinement means forms a confined space in the vicinity of, or incontact with, a specified surface of at least one of the lateral wallsof the shell.
 6. A method according to claim 4, wherein the confinementmeans is contiguous or fixed to the shell or integral therewith.
 7. Amethod according to claim 1, wherein said droplets are produced byspraying said heat transfer fluid.
 8. A method according to claim 7,wherein at least one nozzle is used to carry out said spraying.
 9. Amethod according to claim 1, wherein said heat transfer fluid is water.10. A method according to claim 9, wherein the water is purified.
 11. Amethod according to claim 1, wherein said droplets are mixed with acarrier gas.
 12. A method according to claim 11, carrier gas is used toproduce said droplets by spraying.
 13. A method according to claim 11,wherein said carrier gas is air.
 14. A method according to claim 1,further comprising controlling the heat transfer fluid dropletproduction rate.
 15. A method according to claim 1, wherein saiddroplets have a size between 0.1 and 5 mm.
 16. A method according toclaim 1, wherein the droplets form a mist or aerosol.
 17. A methodaccording to claim 1, wherein the droplets are produced at a specifieddistance D from a wall of the shell less than 20 cm, so as to limit thecoalescence of said droplets before vaporisation in contact with saidwall.
 18. A method according to claim 1 , wherein the confinement meanscomprises at least one casing.
 19. A method according to claim 18,wherein said casing is positioned so that said casing overlaps with anaverage level of interface between the electrolyte bath and the liquidmetal pad.
 20. A method according to claim 1, further comprisingevacuating all or part of heat transfer fluid vapour formed by thevaporisation of all or part of said droplets upon contacting the shell.21. A method according to claim 20, wherein said vapour is evacuated bynatural ventilation, by suction or blowing, or a combination thereof.22. A system of an electrolytic cell intended for aluminium productionby means of igneous electrolysis, said cell comprising a pot comprisinga metal shell having lateral walls and a bottom wall, said pot beingintended to contain an electrolyte bath and a liquid metal pad, whereinsaid system comprises at least one means to produce heat transfer fluiddroplets and a means to place all or part of said droplets in contactwith the shell, so as to induce the vaporisation of all or part of saiddroplets.
 23. A system according to claim 22, further comprising: atleast one confinement casing at a specified distance from at least onewall of the shell, heat transfer fluid supply means, at least one meansto produce heat transfer fluid droplets in said casing, so as to placeall or part of said droplets in contact with the shell.
 24. A systemaccording to claim 23, wherein each confinement casing is at a specifieddistance from at least one lateral wall of the shell less than 20 cm.25. A system according to claim 23, wherein each confinement casing ispositioned so as to overlap with an average level of an interfacebetween the electrolyte bath and the liquid metal pad.
 26. A systemaccording to claim 23, comprising a plurality of confinement casingsdistributed around the shell.
 27. A system according to claim 23,wherein the heat transfer fluid supply means comprise routing means anda treatment column.
 28. A system according to claim 22, wherein saidmeans to produce droplets is a spraying means.
 29. A system according toclaim 28, wherein the spraying means comprises at least one nozzle. 30.A system according to claim 29, wherein said nozzle is an aerosolnozzle.
 31. A system according to claim 22, further comprising at leastone means to supply each confinement casing with carrier gas.
 32. Asystem according to claim 31, further comprising a means to produce saiddroplets using said carrier gas.
 33. A system according to claim 22,further comprising at least one means to control the production rate ofsaid droplets.
 34. A system according to claim 22, further comprisingmeans to evacuate all or part of vaporised heat transfer fluid.
 35. Asystem according to claim 34, wherein the evacuation means compriseevacuation conduits and a suction or blowing means.
 36. A systemaccording to claim 34, wherein the evacuation means comprise a condenserto condense the suspended heat transfer fluid.
 37. A method for coolingan igneous electrolysis aluminium production cell comprising using amethod of claim
 1. 38. A method for cooling an igneous electrolysisaluminium production cell comprising using a system of claim
 22. 39. Amethod to regulate an electrolytic cell intended for aluminiumproduction by means of igneous electrolysis comprising a methodaccording to claim
 1. 40. An electrolytic cell intended for aluminiumproduction by means of igneous electrolysis comprising a cooling systemaccording to claim 22.